SOME EFFECTS OF CARBARYL ON THE GROWTH AND DEVELOPMENT OF APPLE LEAVES: A POSSIBLE MECHANISM FOR FRUITLET THINNING

In experiments involving Jonagold, McIntosh and Fuji apple we have examined the relative effectiveness of carbaryl, 6-benzyladenine (as Accel, Abbott Laboratories) and the combination of both chemicals for reducing fruit set and improving fruit weight and internal quality at harvest.
We also examined spur shoots and leaves in late summer to determine bourse shoot leaf number, total and average leaf area and specific leaf weight.
With Jonagold these spurs supported either 0, 1 or 2 fruits to full maturity.
With McIntosh, single-fruit spurs were located in three canopy zones differing in light exposure.
With Fuji, single-fruit spurs were compared to “resting” spurs.

Carbaryl treatment reduced fruit set in all experiments whereas 6-benzyladenine was largely without effect as a fruitlet thinner.
However, when the two chemicals were combined the reduction in fruit set generally exceeded that achieved with carbaryl alone.

Carbaryl applied 2–3 weeks after full bloom increased specific leaf weight in all three experiments.
On the other hand, McIntosh apples treated with carbaryl at petal fall showed no increase in specific leaf weight at the end of the season even though fruit set was reduced.
In this case bourse shoot leaf number was reduced and average leaf area increased by carbaryl treatment.
There were no effects of 6-benzyladenine on any spur leaf characteristic.

These effects of carbaryl on the growth and development of apple leaves may prove to be a clue to its activity as a fruitlet thinner.

International Symposium on Growth and Development of Fruit Crops

Norman E. Looney

Benzyladerine, NAA, Naphthalenacetic Acid

https://doi.org/10.17660/ActaHortic.2000.527.14